1. Field of the Invention
The present invention relates to pumping devices and methods. More particularly, the present invention relates to hydraulic pumps and methods of hydraulic pumping.
2. Description of Related Art
Hydraulic pumps or hydro-pumps, are used to pump a hydraulic oil from a first pressure level to a second pressure level. These pumps often are supplied by, and deliver from, an oil tank in a closed circuit, so that the oil, after passing through the working section, is admitted back into the oil tank. The oil tanks are designed to be so large that they can accommodate an oil volume corresponding to three to five times the oil volume that is pumped by the pump per minute.
In operation, oil that was beforehand admitted into the tank often carries entrained air with it or air is entrained by the oil during admission of the oil into the tank. Due to the comparatively large tank, the supplied oil resides in the tank for a sufficiently long period of time before it is delivered out of the tank once again. During this residence period, the air entrained in the oil can rise to the surface. When the tank is designed to be correspondingly large, it is possible to ensure that the hydro-pump always draws in oil without entrained air.
However, entrained air is a problem with respect to mobile tanks. The mobile oil tanks are designed to be substantially smaller for reasons of cost and weight, which results in a shorter residence time of the oil in the tank. Due to this, contemporary hydro-pumps draw in foamed oil, that is, oil containing entrained air.
As a result of this unfavorable condition, the space available to the oil in the pressure buildup region of the hydro-pump is not filled completely with oil. Particularly in the case of gear pumps, it is not possible to bring the gear chambers in the reversing phase to the desired system pressure. When the pressure region is entered, the unfilled volumes—the only partially filled gear chambers for gear pumps—are abruptly filled. Local pressure waves are formed that lead to high pulsations. This leads to an extreme noise production and to damage to the structural parts owing to cavitation. Particularly in the pressure buildup region of hydro-pumps, traces of cavitation are repeatedly found.
Accordingly, there is a need to address the problems described above. There is a need for a hydraulic pump and method of hydraulic pumping that reduces or eliminates unwanted noise, local pressure waves, pressure pulsations or cavitation.